It depends on your cultural upbringing- I don’t subscribe to a lot of things my culture advocates but I do like the idea of respecting elders, especially parents- and in Indian culture one’s spouses parents are considered one’s own parents- so in this case the mother-in-law might not have been correct but she should not have been disrespected so blatantly.

The poster did not have to eat the meal but she should not have left in the middle to go to McDonald’s. It’s just plain kindness to turn the other cheek in certain situations- even if the other party is overstepping boundaries you can still maintain your own dignity and classiness and not be rude and mannerless as a guest.